Sum and difference antenna

ABSTRACT

The radiation elements of an antenna comprising a linear array of elements and a further compensation element are fed so that the radiation pattern of a central portion of the linear array is in quadrature of phase with the radiation pattern of the remaining elements of the array, for the formation of a nondirective pattern covering the secondary lobes of the directive pattern obtained through an in-phase feeding of the elements of the linear array.

United States Patent 1111 3,594,81 1

{72] Inventor Robert L. Pierrot 56 References Cit d 53: 3 UNITED STATESPATENTS P 3,160,887 12/1964 Broussaud et al. 1 343/777 [22] Filed Feb.7, 1969 3,255,450 6/1966 Butleri .4 .1 343/854 X [45] Patented July 20,1971 3,267,472 8/1966 Fmk 343/854 X [73] Assrgnee Thomson-CSF [32]Priority Feb. 9 968 3,276,018 9/1966 Butler 343/854 X [33] France3,325,816 6/1967 Dutton 343/777 [31 139 374 Primary Examiner-German KarlSaalbach Assistant Examiner-Marvin Nussbaum AnomeyCushman, Darby andCushman [54] g'fi gg m g ANTENNA ABSTRACT: The radiation elements of anantenna comprising a linear array of elements and a further compensationele- [52] US. Cl 343/854, ment are fed so that the radiation pattern ofa central portion 343/816 of the linear array is in quadrature of phasewith the radiation [51] Int. Cl 01g 3/26, pattern of the remainingelements of the array, for the forma- 1-l01g 3/24, H01 g 21/00 tion of anondirective pattern covering the secondary lobes of [50] Field ofSearch 343/853- the directive pattern obtained through an in-phasefeeding of 4, 837, 777--8, 816 the elements of the linear array.

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O o w Fig.2

PATENTED JUL20 |97| SHEET 2 OF 3 POW R DBTMBUTOQ SW \TH POWER DISTRIBUT0 O O O O O Fig.4-

PATENTEUJULZOIQYI 3,594,811

SHEET 3 OF 3 POWER sou CE /A2 0 P WER 2Q DIETQEETO DLSTRBUTOE I O/ O! 32le 2 e 5e SUM AND DIFFERENCE ANTENNA The present invention relates toantennae of the kind comprising an array of radiating elements, such asfor example dipoles, and means for feeding said array in two difierentways in order to obtain either a pencil beam radiation pattern, alsoreferred to as a sum pattern, of the kind generally produced by in-phasefeeding of all the elements, or a wide radiation pattern covering thesecondary lobes of the pencil beam pattern, this wide pattern also beingreferred to as a difference pattern because of the way in which theindividual elements are generally fed to produce itv Such antennae areused in particular in electromagnetic identification systems of the kindknown as IFF (identification friend or foe) systems or secondary" radarsystems.

A combination of the two radiation patterns is designed essentially toeliminate from the signals picked up by means of the sum pattern, thosedue to the secondary lobes and it is therefore important that thedifference pattern should cover all these lobes. With conventionalantennae, this is not entirely the case.

It is an object of the invention to avoid this drawback.

According to the invention there is provided an antenna systemalternately having a directive radiation patten and a nondirectiveradiation pattern, said system comprising a linear array of radiatingelements located symmetrically with respect to a symmetry plane, an afurther element in said plane; said array comprising a central group ofK elements, including two symmetrical subgroups of K/2 elements if K iseven and two symmetrical subgroups of K-l/Z elements if K is odd, andtwo symmetrical groups of p elements on both sides of said centralgroup, K and p being integers, said system further comprising feedingmeans for alternately (i) for forming said directive radiation pattern,feeding in phase at least the 2p elements of said two symmetrical groupsand (ii) for forming said nondirective radiation pattern,simultaneously: feeding in phase, a first group of n consecutiveelements, located on one side of the central group of elements, n beingan integer smaller than pl-l said first group of n elements, designatedin the following as "lateral" group for the sake of brevity, being apart of one of said groups of p elements; feeding in phase, but in phaseopposition to said first lateral group, a second lateral group of nelements symmetrical with said first lateral group with respect to saidcentral group; feeding, in phase quadrature with respect to said lateralgroups, said further element; and feeding said central group in phasewith either one of said lateral groups if K is odd, and the elements ofsaid two symmetrical subgroups in phase opposition relatively to eachother and in phase quadrature with respect to the elements of thelateral groups if K is even, thereby obtaining a radiation pattern inquadrature of phase with that resulting from the feeding in phaseopposition of said two lateral groups.

For a better understanding of the invention and to show how the same maybe carried into effect, reference will be made to the drawingsaccompanying the following and in which:

FIG. 1 schematically illustrates a plan view of the element array of anantenna in accordance with the invention;

FIG. 2 shows the way in which the various groups of radiators contributeto the difference radiation pattern;

FIG. 3 schematically illustrates an example of an antenna assembly,including the radiator elements and their energizing means;

FIG. 4 illustrates the sum and difference radiation patterns produced bythe antenna of FIG. 3; and

FIG. 5 schematically illustrates another example of an antenna assembly.

By way of example, it will be assumed that the sum pattern produced bythe antenna is narrow in the azimuth plane and wide in elevation. Theradiators of the antenna in accordance with the invention form a regulararray, for example an horizontal array of vertical dipoles, which formtwo groups of p elements (p=8 in the figure), d,, d,...d,,, andd,,...d,,,, regularly spaced on either side of a central group of Kelements; in the figure K has been assumed to be equal to 1 the centralgroup being in the present instance built up by dipole A only.

A radiator D is located at the rear, in a known manner.

The sum pattern, or interrogation pattern in the case of an IFF system,is produced by feeding in phase all the radiators of the array,possibly, if K is odd and for technological reasons, with the exceptionof the elements of the central group. This radiation pattern is shown infull line in FIG. 2.

The difference pattern, or check" pattern in the aforementioned case, isformed by the sum of several elementary patterns:

the pattern produced by feeding in phase opposition the radiator groupsB and C, that is to say the lateral groups of radiators, respectivelycomprising a number of n of successive radiators, this number beingpreferably less than p;

the pattern produced by feeding the radiator D in phase quadrature withrespect to the elements of groups B and a pattern produced by feeding inphase with one of the group B and C the central group if K is odd or byfeeding the two symmetrical parts of the central group in phasequadrature with the groups B and and in phase opposition with respect toeach other if K is even.

The supplies of the radiators, resulting in the formation of twopatterns, respectively directive and broad, can be effected, with K odd,in accordance with the diagram of FIG. 3 where A constitutes the centralgroup, I\' being taken equal to l, and where p is taken equal to eight,the lateral groups B and C of each n=4 elements being parts of the twosymmetrical groups of each p=8 elements, built up respectively by theassemblies B, B, and C, C a power source G feeds a switch R which feedsin turn power-splitters Z and A, the former having two in-phase outputs0', and 0', and the latter two in-phase outputs 0, and 0 and an output 0in phase quadrature with the preceding ones, which feed as shown in FIG.3 two hybrid junctions, for example magic-Tees T, and T, with respectivesum channels 2, and 2, and respective difference channel A, and A,; Zrepresents a matched load, the channel A, not being used.

In FIG. 4, the two antenna radiation patterns corresponding to the twotypes of supply have been shown respectively in full line and brokenline.

In this example, the central group which comprises only the radiator Ais not fed, when the production of the directional radiation pattern isdesired, this in order the avoid a loss of supply energy or acomplication of the circuit. However, it goes without saying that thereis theoretically no reason why this group should not be fed.

The diagram of FIG. 5 is an example of a radiator feeding circuitresulting in the alternate formation of a directive and a broad patternwith K even, the central group then comprising two symmetricalsubgroups: the switch R couples the power source G to two powerdistributors Z, and A, alternately the former having three in-phaseoutputs, 0,,, 0 0 and the latter, two in-phase outputs 0' 0' and anoutput 0',, in phase quadrature with the preceding ones. Outputs 0,,, 0,0,, are coupled respectively to the respective sum channels 2,, 2,, 2,of three four-arm hybrid junctions T,, T,, T,,, whose respectivedifference channels are respectively coupled to output 0',,,, to amatched load and to output 0',,., the remaining channels of junction T,being coupled to the elements of groups B and C respectively, those ofgroups B, and C, and those of junction T, to the symmetrical subgroupsof the central group here reduced respectively to elements a, and aOutput 0' is coupled to element D.

The diagrams of FIGS. 3 and 5 relate to a transmitting antenna; however,the antenna may of course be operated without any structure modificationas a receiver antenna, the principle of reciprocity being in force heresince all the circuits are passive circuits.

The antenna in accordance with the invention makes it possible toachieve a substantial improvement in the ratio between the signalsobtained with the respective two radiation patterns. This means that fora given range, the probability that an associated transponder willrespond is higher, or, that for a given probability of response therange is increased; on the other hand, as already pointed out, theeffective aperture of the beam, as defined by the intersection betweenthe two radiation patterns, is virtually constant due to the fact thatthe slops of the patterns, at their points of intersection, aresubstantially reverse of each other; the aperture angle is moreovercapable of further reduction by reducing the level of the sum pattern inthe central zone.

Of course, the invention is in no way limited to the embodimentsdescribed and illustrated here purely by way of example.

What I claim is:

I. An antenna system alternately having a directive radiation patternand a nondirective radiation pattern, said system comprising a linear ofradiating elements located symmetrically with respect to a symmetryplane, and a further element in said plane, said further element beinglocated outside said linear array; said array comprising a central groupof K elements, including two symmetrical subgroups of l(/2 elements if kis even and two symmetrical subgroups of (K-l/2) Zelements if K is odd,and two symmetrical groups ofp elements on both sides of said centralgroup, K and p being integers, said system further comprising feedingmeans for alternately (i), for fonning the directive radiation pattern:feeding in phase at least the 2p elements of said two symmetrical groupsand (ii), for forming said nondirective radiation pattern,simultaneously: feeding in phase a first lateral group of n consecutiveelements, located on one side of the central group of elements, I: beingan integer smaller than p+l; feeding in phase, but in phase oppositionto said first lateral group, a second lateral group of n elementssymmetrical with said first lateral group with respect to said centralgroup; feeding, in phase quadrature with respect to said lateral groups,said further element; and feeding said central group in phase witheither one of saidlateral groups if K is odd, and the elements of saidtwo symmetrical subgroups in phase opposition relatively to each otherand in phase quadrature with respect to the elements of the lateralgroups if K is even, thereby obtaining a radiation pattern in quadratureof phase with that resulting from the feeding in phase opposition ofsaid two lateral groups.

2. An antenna system according to claim ll, wherein, said central groupcomprising an odd number of elements, said feeding means comprise: apower means having an output;

switching means having an input coupled to said power means output, anda first and a second output; a first power distributor having an inputcoupled to said first output of said switching means and a first and asecond in-phase outputs; a second power distributor having an inputcoupled to said second output of said switching means and a first outputcoupled to said central group, a second output, and a third outputcoupled to said further element, the energy at said third output beingshifted by 77/2 with respect to that at said first and second outputs ofsaid second distributor; a first hybrid junction having a Difierence"channel coupled to said second output of said second distributor, a Sum"channel coupled to said first output of said first distributor, and twofurther channels respectively coupled to said first and second groupsofp elements and a second hybrid junction having a Difference channelcoupled to a matched load, a Sum channel coupled to said second outputof said first distributor, and two further channels respectively coupledto the two groups of consecutive (p-n) elements located symmetricallywith respect to the central group and not including theelements of saidgroups of n channels.

3. An antenna system according to claim 1, wherein, K being even, saidfeeding means comprise: a power means having an output switching meanshaving an input coupled to said power means output, and a first an asecond ou put; a first power distributor having an input coupled to saidfirst output of said switching means, a first, a second and a thirdin-phase outputs; a second power distributor having an input coupled tosaid second output of said switching means, a first output, a secondoutput coupled to said further element and a third output, the energy atsaid last mentioned first output being in quadrature of phase withrespect to that at said last mentioned second and third outputs; a firsthybrid junction having a "Difference" channel coupled to said firstoutput of said second distributor, a Sum" channel coupled to said firstoutput of said first distributor and two further channels respectivelycoupled to said first and second group of n elements; a second hybridjunction having a difference channel coupled to a matched load; a Sumchannel coupled to said second output of said first distributor, and twofurther channels respectively coupled to the two groups of consecutive(p-n) elements located symmetrically with respect to the central groupand not including the elements of said lateral groups ofn elements; anda third hybrid junction having a Difference channel coupled to saidsecond output of said third distributor, a Sum channel coupled to saidthird output of said first distributor and two further channels coupledto the elements of said two subgroups respectively.

1. An antenna system alternately having a directive radiation patternand a nondirective radiation pattern, said system comprising a linear ofradiating elements located symmetrically with respect to a symmetryplane, and a further element in said plane, said further element beinglocated outside said linear array; said array comprising a central groupof K elements, including two symmetrical subgroups of K/2 elements if kis even and two symmetrical subgroups of (K-1/2) 2elements if K is odd,and two symmetrical groups of p elements on both sides of said centralgroup, K and p being integers, said system further comprising feedingmeans for alternately (i), for forming the directive radiation pattern:feeding in phase at least the 2p elements of said two symmetrical groupsand (ii), for forming said nondirective radiation pattern,simultaneously: feeding in phase a first lateral group of n consecutiveelements, located on one side of the central group of elements, n beingan integer smaller than p+1; feeding in phase, but in phase oppositionto said first lateral group, a second lateral group of n elementssymmetrical with said first lateral group with respect to said centralgroup; feeding, in phase quadrature with reSpect to said lateral groups,said further element; and feeding said central group in phase witheither one of said lateral groups if K is odd, and the elements of saidtwo symmetrical subgroups in phase opposition relatively to each otherand in phase quadrature with respect to the elements of the lateralgroups if K is even, thereby obtaining a radiation pattern in quadratureof phase with that resulting from the feeding in phase opposition ofsaid two lateral groups.
 2. An antenna system according to claim 1,wherein, said central group comprising an odd number of elements, saidfeeding means comprise: a power means having an output; switching meanshaving an input coupled to said power means output, and a first and asecond output; a first power distributor having an input coupled to saidfirst output of said switching means and a first and a second in-phaseoutputs; a second power distributor having an input coupled to saidsecond output of said switching means and a first output coupled to saidcentral group, a second output, and a third output coupled to saidfurther element, the energy at said third output being shifted by pi /2with respect to that at said first and second outputs of said seconddistributor; a first hybrid junction having a ''''Difference'''' channelcoupled to said second output of said second distributor, a ''''Sum''''channel coupled to said first output of said first distributor, and twofurther channels respectively coupled to said first and second groups ofp elements and a second hybrid junction having a Difference channelcoupled to a matched load, a Sum channel coupled to said second outputof said first distributor, and two further channels respectively coupledto the two groups of consecutive (p-n) elements located symmetricallywith respect to the central group and not including the elements of saidgroups of n channels.
 3. An antenna system according to claim 1,wherein, K being even, said feeding means comprise: a power means havingan output switching means having an input coupled to said power meansoutput, and a first and a second output; a first power distributorhaving an input coupled to said first output of said switching means, afirst, a second and a third in-phase outputs; a second power distributorhaving an input coupled to said second output of said switching means, afirst output, a second output coupled to said further element and athird output, the energy at said last mentioned first output being inquadrature of phase with respect to that at said last mentioned secondand third outputs; a first hybrid junction having a ''''Difference''''channel coupled to said first output of said second distributor, a''''Sum'''' channel coupled to said first output of said firstdistributor and two further channels respectively coupled to said firstand second group of n elements; a second hybrid junction having adifference channel coupled to a matched load; a Sum channel coupled tosaid second output of said first distributor, and two further channelsrespectively coupled to the two groups of consecutive (p-n) elementslocated symmetrically with respect to the central group and notincluding the elements of said lateral groups of n elements; and a thirdhybrid junction having a Difference channel coupled to said secondoutput of said third distributor, a Sum channel coupled to said thirdoutput of said first distributor and two further channels coupled to theelements of said two subgroups respectively.